1. Field of the Invention
The present invention relates to transducers that convert pressure variations into electrical output signals and more specifically to transducers utilizing electro-optic sensors in a fiber optic system.
2. Description of the Prior Art
Fiber optic transducers responsive to ambient conditions ordinarily utilize a membrane that is deflected by variations in ambient conditions such as atmospheric pressure. The membrane is coupled to one or more optical fibers having opposing end faces disposed on either side of an air gap. Motion of the membrane distorts the fibers and causes a variation of the coupling of the light across the air gap which can be detected and measured electronically.
Co-pending patent application Ser. No. 248,616, now abandoned, filed in the name of D. H. McMahon and assigned to the present assignee concerns a transducer that utilizes the birefringent properties of elast-optic materials to measure ambient conditions such as temperature, pressure or acceleration. Light is coupled from a source to a collimating lens through an optical fiber. The light from the lens is applied to a polarizer oriented at 45.degree. to the vertical and thence to an elasto-optic material such as glass. Lucite or Plexiglass which becomes birefringent under applied mechanical stress. The birefringence creates a difference in phase between the vertical and horizontal components of the polarized light which is a function of the stress applied to the elasto-optic material. The phase shifted components are further processed and applied to optical detectors which provide an electrical signal indicative of the phase difference between the vertical and horizontal components and therefore the stress applied to the elasto-optic material.
The device of the present invention employs an elasto-optic sensor similar to the McMahon device but provides greatly improved sensitivity and linearity by utilizing a novel null balance technique.